Abstract: A research on cellular instability of outwardly propagating spherical premixed flame was carried out on constant volume combustion bomb with schlieren method by using high speed camera and data acquisition. The developing process, causes and influence factors of flame cellular instabilities was analyzed. The results showed that the cellular instabilities mainly included unequal diffusion instability and hydrodynamic instability. The cause of hydrodynamic instability was that stream lines integrated or diverged due to curvature reason, so the velocity of the flow field increases or decreased. The flame thickness and density ratio of burned to unburned zone were the main influence factors of hydrodynamic instability. The cracks and regular distortions of the flame surface was the main phenomenon. The cause of unequal diffusion instability was that thermal-mass unequal diffusion of the flame front control volume. The Lewis number was the main influence factor, and the phenomenon of unequal diffusion instability was un-regular distortions of the flame surface.